The present invention relates to a device for programming an implantable electrode array used with an implantable stimulator. More particularly, one embodiment of the invention relates to a device used to provide directional programming for the implantable electrode array associated with an implantable stimulator that electrically stimulates the spinal cord for the purposes of controlling and reducing pain.
Within the past several years, rapid advances have been made in medical devices and apparatus for controlling chronic intractable pain. One such apparatus involves the implantation of an electrode array within the body to electrically stimulate the area of the spinal cord that conducts electrochemical signals to and from the pain site. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. One theory of the mechanism of action of electrical stimulation of the spinal cord for pain relief is the xe2x80x9cgate control theoryxe2x80x9d. This theory suggests that by simulating cells wherein the cell activity counters the conduction of the pain signal along the path to the brain, the pain signal can be blocked from passage.
Spinal cord stimulator and other implantable tissue stimulator systems come in two general types: xe2x80x9cRFxe2x80x9d controlled and fully implanted. The type commonly referred to as an xe2x80x9cRFxe2x80x9d system includes an external transmitter inductively coupled via an electromagnetic link to an implanted receiver that is connected to a lead with one or more electrodes for stimulating the tissue. The power source, e.g., a battery, for powering the implanted receiver-stimulator as well as the control circuitry to command the implant is maintained in the external unit, a hand-held sized device that is typically worn on the patient""s belt or carried in a pocket. The data/power signals are transcutaneously coupled from a cable-connected transmission coil placed over the implanted receiver-stimulator device. The implanted receiver-stimulator device receives the signal and generates the stimulation. The external device usually has some patient control over selected stimulating parameters, and can be programmed from a physician programming system. An example of an RF system is described, e.g., in U.S. Pat. No. 4,793,353, incorporated herein by reference.
The fully implanted type of stimulating system contains the programmable stimulation information in memory, as well as a power supply, e.g., a battery, all within the implanted pulse generator, or xe2x80x9cimplantxe2x80x9d, so that once programmed and turned on, the implant can operate independently of external hardware. The implant is turned on and off and programmed to generate the desired stimulation pulses form an external programming device using transcutaneous electromagnetic, or RF links. Such stimulation parameters include, e.g., the pulse width, pulse amplitude, repetition rate, and burst rates. An example of such a commercially-available implantable device is the Medtronic Itrel II, Model 7424. Such device is substantially described in U.S. Pat. No. 4,520,825, also incorporated herein by reference.
The ""825 patent describes a circuit implementation of a cyclic gradual turn on, or ramping of the output amplitude, of a programmable tissue stimulator. The implementation contains separate memory cells for programming the output amplitude and number of pulses at each increasing output level or xe2x80x9cstepxe2x80x9d. In devices of the type described in the referenced ""825 patent, it is desirable to provide some means of control over the amplitude (intensity), the frequency, and the width of the stimulating pulses. Such control affords the patient using the device the ability to adjust the device for maximum effectiveness. For example, if the pulse amplitude is set too low, there may be insufficient pain relief for the user; yet, if the pulse amplitude is set too high, there may be an unpleasant or uncomfortable stinging or tingling sensation felt by the user. Moreover, the optimum stimulation parameters may change overtime. That is, numerous and varied factors may influence the optimum stimulation parameters, such as the length of time the stimulation has been ON, user (patient) postural changes, user activity, medicines or drugs taken by the user, or the like.
In more complex stimulation systems, one or more leads can be attached to the pulse generator, with each lead usually having multiple electrode contacts, Each electrode contact can be programmed to assume a positive (anode), negative (cathode), or OFF polarity to create a particular stimulation field when current is applied. Thus, different combinations of programmed anode and cathode electrode contacts can be used to deliver a variety of current waveforms to stimulate the tissue surrounding the electrode contacts.
Within such complex systems, once one or more electrode arrays are implanted in the spinal cord, the ability to create paresthesia over the painful site is firstly dependent upon the ability to accurately locate the stimulation site. This may more readily be accomplished by programming the selection of electrode contacts within the array(s) than by physically maneuvering the lead (and hence physically relocating the electrode contacts). Thus, the electrode arrays may be implanted in the vicinity of the target site, and then the individual electrode contacts within the array(s) are selected to identify an electrode contact combination that best addresses the painful site. In other words, electrode programming may be used to pinpoint the stimulation area correlating to the pain. Such electrode programming ability is particularly advantageous after implant should the lead contacts gradually or unexpectedly move, thereby relocating the paresthesia away from the pain site. With electrode programmability, the stimulation area can often be moved back to the effective site without having to re-operate on the patient in order to reposition the lead and its electrode array.
Electrode programming has provided different clinical results using different combinations of electrode contacts and stimulation parameters, such as pulse width, amplitude and frequency. Hence, an effective spinal cord stimulation system should provide flexible programming to allow customization of the stimulation profile for the patient, and thereby allow for easy changes to such stimulation profile over time, as needed.
The physician generally programs the implant, external controller, and/or external patient programmer through a computerized programming station or programming system. This programming system can be a self-contained hardware/software system, or can be defined predominately by software running on a standard personal computer (PC). The PC or custom hardware can have a transmitting coil attachment to allow for the programming of implants, or other attachments to program external units. Patients are generally provided hand-held programmers that are more limited in scope than are the physician-programming systems, with such hand-held programmers still providing the patient with some control over selected parameters.
Programming of the pulse generators, or implants, can be divided into two main programming categories: (1) programming of stimulation pulse variables, and (2) programming electrode configurations. Programmable stimulation pulse variables, as previously indicated, typically include pulse amplitude, pulse duration, pulse repetition rate, burst rate, and the like. Programmable electrode configuration includes the selection of electrodes for simulation from the available electrode contacts within the array as well as electrode polarity (+/xe2x88x92) assignments. Factors to consider when programming an electrode configuration include the number of electrode contacts to be selected, the polarity assigned to each selected electrode contact, and the location of each selected electrode contact within the array relative to the spinal cord, and the distance between selected electrodes (anodes and cathodes), all of which factors combine to define a stimulation field. The clinician""s electrode selection results in a simulating xe2x80x9cgroupxe2x80x9d containing at least one anode and at least one cathode that can be used to pass stimulating currents defined by the programmed pulse variables. For an electrode array having eight electrode contacts, this can result in an unreasonable large number of possible combinations, or stimulation groups, to chose from.
Moreover, within each stimulation group, there are a large number of pulse stimulation parameters that may be selected. Thus, through the programmer, the clinician must select each electrode, including polarity, for stimulation to create each combination of electrode contacts for patient testing. Then, for each combination, the clinician adjusts the stimulation parameters for patient feedback until the optimal pain relief is found for the patient. Disadvantageously, it is difficult to test many stimulation variables with hundreds or even thousands of possible electrode and stimulus parameter combinations. To test all such combinations, which is typically necessary in order to find the optimum stimulation settings, is a very lengthy and tedious process. Because an all-combination test is lengthy and tedious, some clinicians may not bother to test many different electrode combinations, including many that may be considered far more optimal than what is ultimately programmed for the patient. It is thus evident that there is a need in the art for a more manageable programming technique for testing and handling a large number of possible electrode and pulse parameter combinations.
One method that has recently been developed for simplifying the programming process is described in U.S. Pat. No. 5,370,672, incorporated herein by reference. The ""672 patent describes a programming system where the patient interacts with the clinician""s programmer. More specifically, the ""672 patent teaches a system wherein the patient identifies the pain site by xe2x80x9cdrawingxe2x80x9d the pain site on a touch screen that displays an illustration of the human body. After entering the patient""s stimulation thresholds and associated tolerances into the system, the computer generates a recommended electrode configuration for that patient using algorithms based on spinal cord stimulation research. The patient responds to the resulting stimulation by drawing the amount of paresthesia coverage over the body illustration. If the drawing paresthesia site does not fully match the pain site, the system adjusts the recommendation, and the patient responds again to the new sense of paresthesia. This process is repeated until the best-tested settings are reached.
Advantageously, the process described in the ""672 patent effectively eliminates the manual selection of electrode combinations, and reduces the selection process to a reasonable testing of electrode/parameter combinations based on an extensive pre-organized set of rules for programming optimization and patient input. Moreover, the physician/clinician is not directly controlling the programming session; rather, the patient provides the system with the feedback without the need for the physician or clinician to interpret the patient""s sensations or empirically estimate changes required in stimulation parameters.
Disadvantageously, using the method described in the ""672 patent, the patient must still test and respond to each of the chosen combinations and must depend upon the system recommendations, which system recommendations might exclude a possible optimal setting for that patient. Further, the patient must be able to accurately translate subtle sensations and differences to a drawing on a screen, and then wait for device programming before having to react and redraw the paresthesia from the new settings. Such process can still be time consuming. Furthermore, subtle sensation differences felt by the patient between combinations cannot necessarily be translated in a drawing of paresthesia that only address xe2x80x9ccoverage area.xe2x80x9d In summary, by reducing the combinations to a computer-generated recommendation, many electrode combinations might be omitted that could provide a more effective paresthesia. Hence, the process of computer-recommended combinations, although superior to manual arbitrary selection, can still be viewed as an undesirable xe2x80x9cdiscretexe2x80x9d method of patient feedback evaluation: i.e., electrodes are programmed and patient feedback is entered for each combination, one iteration at a time.
In view of the above, it is evident that profound improvements are still needed in the way multiple implanted electrode combinations are programmed. In particular, it is seen that improvements in programming techniques and methods are needed that do not compromise the patient""s ability to feel the subtle effects of many different combinations, and that provide a more immediately responsive programming-to-feedback loop.
The present invention advantageously addresses the needs above, as well as other needs, by providing improved programming methods for electrode arrays having a multiplicity of electrodes. The present invention advantageously simplifies the programming of multiple electrode contact configurations by using a directional input device in conjunction with a programmer/controller to automatically combine and reconfigure electrodes with alternating current paths as determined by the directional input device. The directional input device used with the invention may take many forms, e.g., a joystick, a button pad, a group of keyboard arrow keys, a touch screen, a mouse, or equivalent directional input mechanisms. Advantageously, the use of a directional input device to automatically adjust electrode configurations in order to xe2x80x9csteerxe2x80x9d the stimulation current allows the patient to immediately feel the effect of electrode configuration changes. Then, without having to translate the subtle differences of sensation to a drawing for discrete computer-generated recommendations, or manually and arbitrarily selecting different combinations, the patient responds continuously to the sensation by steering directional or equivalent controls. Hence, the patient more directly controls the programming without being cognizant of actual electrode combinations and variables. The patient is also more immediately responsive, since there is no need to translate the perceived sensations to specific locations on a displayed drawing. This process is thus analogous to continuous feedback as opposed to discrete feedback and system manipulation.
While the directional programming device provided by the invention is primarily intended to program implanted stimulator devices having at least two electrode contacts, it should also be noted that it can also be used to program the electrodes used with external stimulators.
The invention described herein thus relates, inter alia, to a method of programming utilizing directional input signals to xe2x80x9csteerxe2x80x9d and define current fields through responsive automated electrode configuring. Hence, in accordance with one aspect of the invention, programming equipment is utilized including a computer and/or custom transmitter, coil and programming software to achieve the desired current field steering effect. Additional control mechanisms (software and/or hardware) are used to respond to directional control signals generated, e.g., with a joystick or other directional means, so as to configure and combine the electrodes as directed by the joystick or other directional-setting device so as to redistribute the current/voltage field in a way that prevents the paresthesia felt by the patient from either falling below a perceptual threshold or rising above a comfort threshold. As needed, one or more other input devices can be used to control different aspects of the electrode configuration.
In accordance with another aspect of the invention, a representation of the changing current fields resulting from movement of the directional device is visually provided on a display screen associated with the programming equipment, thereby providing visual feedback to the user as to the electrode configurations and/or resulting stimulation fields that are achieved through manipulation of the directional input mechanism.
In use, a spinal cord stimulator is implanted with one or more leads attached to the spinal cord. The implanted spinal cord stimulator is coupled through an RF or other suitable link to the external spinal cord stimulation system, which system is used to program and/or control the implanted stimulator. The style and number of leads are entered into the system software. The clinician then maneuvers the joystick, or other directional instructor, to redirect current to different groups of implanted electrodes. The software then automatically reconfigures electrodes according to directional responsive rules in the software and/or electronics. Automatic configuring of the electrodes to steer current includes, e.g., the number of electrodes, the selection of electrodes, the polarity designation of individual electrodes, and the distribution of stimulation intensities among the selected electrodes.
The advantage achieved with the programming system provided by the invention is that the clinician never has to actually select and test a multitude of electrode combinations with the patient, which otherwise takes time for each configuration. Instead, the patient immediately responds to maneuvers conducted by himself/herself or the clinician, which causes the user to move toward or away from certain directions. The directional programming feature may also be made available directly to the patient through a small portable programming device. Advantageously, all reconfiguring of the electrodes is done automatically as a function of the directional signals generated by the joystick or other directional device(s), and is done in a way that prevents the paresthesia felt by the patient from falling below the perceptual threshold or rising above the comfort threshold.
One embodiment of the invention may be viewed as a programming system for use with a neural stimulation system. Such neural stimulation system includes: (1) a multiplicity of implantable electrodes adapted to contact body tissue to be stimulated; (2) an implantable pulse generator connected to each of the multiplicity of electrodes, the implantable pulse generator having electrical circuitry responsive to programming signals that selectively activates a plurality of the implantable electrodes, wherein at least one electrode in the plurality of activated implantable electrodes functions as a cathode, and wherein at least one electrode in the plurality of activated implantable electrodes functions as an anode, whereby stimulus current flows from the at least one activated anodic electrode to the at least one activated cathodic electrode; (3) a programming device coupled with the implantable pulse generator, the programming device having control circuitry that generates programming signals adapted to control the implantable pulse generator; (4) an input device coupled with the programming device, wherein the input device generates directional signals as a function of user control; and (5) control logic within the programming device that continuously activates selected ones of the multiplicity of implantable electrodes in response to the directional signals received from the user controlled input device, whereby stimulus current is selectively redistributed among cathodic and anodic electrodes as directed by the user controlled input device. The electrical circuitry within the implantable pulse generator may activate the selected electrodes by forcing a prescribed current to flow into (a current sink) a cathodic electrode, by forcing a prescribed current to flow from (a current source) an anodic electrode, by causing a prescribed positive voltage to be applied to an anodic electrode, by causing a prescribed negative voltage to be applied to a cathodic electrode, or by combinations of the above.
It is thus a feature of the present invention to provide a system and a method for programming that allows a clinician or patient to quickly determine a desired electrode stimulation pattern, including which electrodes of a multiplicity of electrodes in an electrode array should receive a stimulation current, the polarity, distance between anodes and cathodes, and distribution of stimulation intensity or amplitude.
It is another feature of the invention to provide an electrode selection system that allows the user (the person operating the programmer) to readily select and visualize a particular group of electrodes of an electrode array for receipt of a stimulation pulse current, and when selected to allow different combinations of pulse amplitude, pulse width, pulse repetition rate, or other pulse-defining parameters to be applied to the selected group.
It is yet an additional feature of the invention to allow an implantable tissue stimulator, having an array of stimulation electrodes attached thereto, to be readily and quickly programmed so that only those electrodes which prove most effective for a desired purpose, e.g., pain relief, are selected and configured to receive a pulsed current having an amplitude, width, repetition frequency, or burst parameters that best meets the needs of a particular patient.
It is still another feature of the invention to provide a system and a method of steering or programming the perceived paresthesia so that any needed redistribution of the stimulus current occurs in small step sizes, thereby making neural recruitment more effective. In accordance with this feature of the invention, the small step size in current or voltage amplitude settings that is used amongst the electrode contacts is selected to effectively correspond to the spatial resolution to which neural elements can be activated. That is, this spatial resolution is meaningful to the extent that the micro-anatomy of the neural structures being activated gives rise to different clinical effects. Advantageously, by using such a system that automatically redistributes current or voltage amplitudes amongst electrodes in suitable small step sizes, desired neural activation patterns may be found more easily.
It is another feature of the invention to provide a system for redistributing current and/or voltage amplitudes amongst selected electrodes using a user interface that is simple and intuitive.
It is an object of the invention to eliminate the need for either a clinician to manually select electrode combinations, or even for a computer to select electrode combinations that must be discretely tested for patient feedback. That is, based on the feedback as to the amount of coverage, an educated guess for another combination must be made (by clinician or computer) and the patient must then discretely respond to that combination before another combination is set up and turned on. Such discrete testing with patient feedback is very tedious and time consuming. Advantageously, by practicing the present invention, discrete selection and patient feedback of location and amount of paresthesia coverage (either to the clinician or to a computer) is avoided.